Hearing assistance devices may have one or more microphones. In examples where two or more microphones receive signals, it is possible to have significantly different microphone responses for each microphone. Such systems are referred to as having “unmatched” microphones. Microphone mismatch can degrade the directional performance of the receiving system. In particular, it can diminish the ability of a manufacturer to control the directional reception of the device. Adjustment at the time of manufacture is not always reliable, since microphone characteristics tend to change over time. Adjustment over the course of use of the hearing device can be problematic, since the sound environment in which adjustments are made can vary substantially.
Microphone mismatch can be particularly problematic in designs of wearable directional devices which have configurations known as “optimal first-order directional microphone designs.” Such mismatches can affect microphone directionality and can result in degradation of the directionality index, especially at low frequencies.
At least three approaches to microphone mismatch have been attempted. One approach is to use only directional microphones with a single diaphragm to reduce mismatch. This approach is limited, since it can be difficult to implement in higher than first order designs. Another approach is to use a suboptimal design to reduce the effect of microphone mismatch. However, this approach naturally sacrifices performance for reliability and cannot tolerate substantial mismatches. Another approach is to use electronics to estimate and compensate for the mismatch using environmental sounds. However, this approach is susceptible to changes in environmental conditions.
Thus, there is a need in the art for improved method and apparatus for microphone matching for wearable directional hearing assistance devices. The resulting system should provide reliable adjustment as microphones change. The system should also provide adjustments which are reliable in a varying sound environment.